In the manufacture of microelectronic devices and circuits, one of the evident needs is for electrically conductive connections between such devices and circuits. As known to those familiar with this technology, in present manufacturing techniques and structures, such connections often take the form of thin layers of metal. These layers are applied in various processes, such as photolithography, in appropriate patterns to form the desired electrical interconnection lines of the device or circuit. Because of the very small dimensions involved, however, repair or replacement of such conductive connecting lines is extremely difficult or impossible under most circumstances.
Additionally, as circuit dimensions decrease in very large scale integration (VLSI) devices, process limitations based upon an allowed thermal budget become increasingly important. Expressed somewhat generally, the thermal budget of a process is the combination of energy and time that must be invested to carry it out. Under most circumstances, lower thermal budgets are preferred over higher ones. As a result, methods of forming metallic thin films at relatively lower temperatures for purposes such as line interconnection are being widely investigated. Among these, one of the simplest and of lowest cost under certain circumstances is metal-organic chemical vapor deposition (MOCVD). A typical MOCVD technique is based upon the decomposition of a vaporized metal-organic compound through the application of some form of energy, for example heat or electromagnetic radiation, that results in the deposition of a metal, an alloy, or a compound in the form of a thin film.
A number of investigations have been carried out and corresponding techniques developed for chemical vapor deposition of metal-organic compounds. Although many of these have become useful for certain purposes, they have not been suitable for repair of electrical connections for a number of reasons.
For example, a number of the MOCVD processes have been developed as methods to repair mask templates in which the goal of depositing the metal from the metal-organic compound is to produce an opaque spot on the mask. It will be understood by those familiar with microelectronic devices and circuits, however, that the amount and characteristics of a material that may produce an opaque spot on a mask, are not nearly as specific as those required for electrical conductivity.
Additionally, to be useful in certain processes, the metal-organic compound must exhibit an appropriate chemical stability under the desired process parameters, must be volatile at a reasonable temperature without decomposition, and must have a sufficient vapor pressure at moderate temperatures to make the MOCVD process worthwhile for the particular application.
Furthermore, from a practical standpoint, and particularly for commercial applications, the deposition must take place at a reasonable rate. Accordingly, deposition processes that are theoretically or experimentally interesting may not be appropriate for commercial applications where the rate of deposition is an important standard.
Perhaps most importantly, particular metals are often either desired or even necessary in the wiring portions of devices and circuits. Electronic circuits are designed and fabricated on the basis of known properties of the interconnecting wiring, and any materials which are used to form or repair such wiring must similarly provide these properties. In particular, many line interconnection applications require copper because of its particular conductivity, impedance, and other related electrical characteristics.
In attempting MOCVD of copper, however, a number of problems exist. First, many of the organic ligands which can successfully be used to make metal-organic compounds suitable for MOCVD with other metals, simply do not form compounds with copper (e.g., for practical purposes copper carbonyls do not exist), or form compounds that are useless for all practical purposes (e.g. copper alkyls often tend to be nonvolatile). Therefore, many of the types of compounds and reactions used with other metals are not analogously available with copper.
Finally, for various reasons a thermally activated MOCVD process would be advantageous. Many of the present processes are instead photochemically initiable. Such a process would be useful in situations where photoexposure is undesired, unavailable, or must be avoided. For example, in CVD processes, photodecomposition of source species is often preferably avoided, and thermally initiated reactions often form better deposits.
Therefore, there exists the need for a method of placing or repairing copper conductive lines in microelectronic devices and circuits which is thermally activated, nonphotochemical, and which deposits copper in an amount, purity, and at a rate reasonable to produce such wiring connections in commercially useful processes.